Telescopic type hydraulic actuators are known that comprise a body defining a cylindrical cavity and a rod extending through one end of the cavity and secured to a piston that is mounted to slide axially inside the cavity so as to define two hydraulic chambers therein. During movement of the rod, it is known to organize throttling at the outlet from the chamber through which the fluid is expelled in order to provide hydraulic damping. Such throttling establishes resistance that is proportional to the square of the travel speed of the rod.
Electrohydraulic actuators are also known that comprise an electric pump that is arranged to transfer fluid from one chamber to the other of the actuator. It is also possible to organize damping by throttling the fluid being expelled from one of the chambers while the rod is moving. Nevertheless, such an actuator is not capable of operating in an emergency with the rod being driven by the load to which it is coupled, unless the pump is reversible and is capable of being released.
Mechanical actuators are also known that comprise a screw extending inside the rod to co-operate with a nut secured to the rod, the screw being driven in rotation by a motor, with rotation of the screw causing the rod to move axially. In such actuators, damping may be provided by organizing resistance to movement of the rod, e.g. of the friction or electromagnetic type. Nevertheless, the first type of resistance is essentially independent of the travel speed of the rod, while the second type of resistance is quite difficult to organize and is generally a function of the travel speed of the rod, which may be found to be insufficient in certain applications. In addition, such dampers give rise to numerous problems in service, such as wear or lack of reliability.